1. Field of the Invention
The present invention relates to an injection molding machine and particularly to a nozzle touch mechanism of the injection molding machine.
2. Description of Related Art
In an injection molding machine for molding a product by injecting molten material such as resin and metal into a cavity formed by a stationary mold and a movable mold from a nozzle provided at a distal end of a heating cylinder of an injection mechanism, a nozzle touch mechanism is provided for moving the injection mechanism relatively to a stationary platen to which the stationary mold is attached so that the nozzle is pressed towards and retracted from a spool of the stationary mold.
FIG. 11 shows a conventional nozzle touch mechanism of an injection molding machine. In FIG. 11, a stationary mold 40 is attached to a stationary platen 30 and a bearing unit 31 for supporting one end of a ball-screw shaft 61 rotatably but axially unmovably is fixed to the stationary platen 30. The other end of the ball-screw shaft 61 is connected to an output shaft of a motor 65 through a coupling 64. A ball-screw nut 62 is threadedly engaged with the ball-screw shaft 61 and supported unrotatably with respect to an extruder bed 20. A spring 63 is intervened between the ball-screw nut 62 and the extruder bed 20. An injection mechanism 10 is mounted on the extruder bed 20 and connected thereto via a swivel pin 21 for a swivel motion. The extruder bed 20 is guided by a linear guide having a guide rod or rail, not shown, movably close to and away from the stationary platen 30. Thus, the injection mechanism 10 is allowed to linearly move towards and away from the stationary platen 30 with the extruder bed 20 and also to swivel about the swivel pin 21 on the extruder bed 20.
For performing a nozzle touch, the motor 65 is driven to rotate the ball-screw shaft 61 such that the ball-screw nut 62 which is unrotatably supported moves forward to the stationary platen 30 (right-hand direction in FIG. 11). The ball-screw nut 62 moves the extruder bed 20 forward through the spring 63 so that a nozzle 10a at a distal end of a heating cylinder 10b of the injection mechanism 10 touches a spool of the stationary mold 40 attached to the stationary platen 30. The servomotor 65 is continuously driven after the nozzle 10a touches the spool of the mold 40 to forward the ball-screw nut 62 to make the spring 63 compressed to urge the extruder bed 20 and the injection mechanism 10 toward the stationary platen 30 so that the nozzle 10a presses the mold 40 by an elastic force of the spring 63. This pressing force applied from the nozzle 10a to the spool of the stationary mold 40, i.e. a nozzle tough force is transmitted from the stationary mold 40 to the stationary platen 30 to produce a moment to incline the stationary platen 30 and the stationary mold 40 as shown by the dotted line in FIG. 11.
The inclination of the stationary mold 40 causes opposing faces of a movable mold (not shown) and the stationary mold 40 to be nonparallel to each other, which may raise a problem of damaging pins guide holes provided at the opposing faces by an interference between them in clamping the molds by a clamping mechanism.
In order to solve the above problem, there is known from Japanese Patent Publication No. 9-277306 a nozzle tough mechanism for preventing a bending moment on the stationary mold by the nozzle tough force by fixing one end of a rotation/linear-motion converting mechanism such as the ball screw mechanism on the stationary platen laterally with respect to a position of the nozzle tough.
FIGS. 12a and 12b are a plan view and a side view, respectively, of the nozzle touch mechanism known from Japanese Patent Publication No. 9-277306 for preventing the bending moment on the stationary platen.
In FIGS. 12a and 12b, the same or equivalent member as shown in FIG. 11 is indicated by the same reference numeral and a reference numeral 32 denotes a fixing member for fixing one end of the ball-screw shaft 61 on the stationary platen 30. As seen from FIGS. 12a and 12b, fixing points of the ball-screw shafts 61 are arranged at opposite positions with respect to the nozzle touch position. Specifically, levels of the fixing points of the ball-screw shafts 61 are substantially the same as the level of the nozzle touch position.
Forward and backward motions of the injection mechanism close to and away from the stationary platen 40 are performed by a rotation of the motor 65. The rotation of the motor 65 is transmitted to the ball-screw nuts 62 through a gear transmission mechanism 66 to rotate the ball-screw nuts 62 in synchronism with each other. Since the ball-screw nuts 62 are supported by the injection mechanism 10 to be rotatable but unmovable in the axial direction of the ball-screw shafts 61 relative to the injection mechanism 10, and the ball-screw shafts 61 are fixed to the stationary platen 30, the ball-screw nuts 62 are moved in the axial direction by a lead of the ball-screw shaft with one rotation thereof. With the axial motion of the ball-screw nuts 62, the injection mechanism 10 connected fixedly with respect to the axial direction is moved forward and backward with respect to the stationary platen 30. When the nozzle 10a at the distal end of the heating cylinder 10b touches the spool of the stationary mold 40 attached to the stationary platen 30 and applies pressure to the spool, no bending moment is produced on the stationary platen 30 since the stationary platen 30 is connected to the ball-screw shafts 61 at the same-level as that of application of the nozzle touch force, so that the stationary platen 30 and the stationary mold 40 are prevented from being inclined.
In the nozzle touch mechanism for preventing the stationary mold and the stationary platen from being inclined by the nozzle touch force as shown in FIGS. 12a and 12b, the ends of the ball-screw shafts have to be arranged on opposite positions on the stationary platen at the same level as that of the nozzle touch position on the stationary mold. This means that the ball-screw shafts are arranged parallel with each other at the same level as that of the heating cylinder of the injection mechanism. Further, the ball-screw nuts have to be driven in synchronism with each other to exert driving force to the injection mechanism 10 at the same speed. To meet these requirements, there arises a problem that the driving mechanism of the nozzle touch mechanism is complicated.
Further, the ball screw mechanisms arranged on both sides of the heating cylinder are inconvenient in maintenance and inspection of the heating cylinder. In order to carry out the maintenance and inspection of the heating cylinder including an exchange of the heating cylinder or the injection screw for a new one, it is necessary to retract the injection mechanism to the position where the nozzle does not interfere with the stationary platen 30 and swivel the injection mechanism on the extruder bed 20 about the swivel pin 21. The above arrangement requires removal of the connection between the stationary platen 30 and the ball-screw shafts 61 of the ball-screw mechanism as a rotation/linear-motion converting mechanism. Furthermore, after finishing the maintenance or inspection, it is necessary to adjust the center of the ball-screw shaft of the ball screw mechanism to retrieve the operational state, so that operations for the maintenance and inspection of the heating cylinder are made laborious.
An object of the present invention is to provide an injection molding machine capable of preventing inclination of a mold and a stationary platen by a nozzle touch force and carrying out maintenance and inspection of the injection mechanism with ease.
An injection molding machine of the present invention comprises a nozzle touch mechanism for moving an injection mechanism relatively to a mold attached to a stationary platen so that a nozzle of a heating cylinder touches and pushes a spool of the mold. The nozzle touch mechanism has a support member for supporting the injection mechanism to be movable, and a driving unit arranged lower than a heating cylinder of the injection mechanism for moving the injection mechanism supported by the support member, and a connection member for connecting the stationary platen with the driving unit. The connection member and the stationary platen are connected at symmetrical positions with respect to a central axis of the nozzle. With the above arrangement, a nozzle touch force exerted on the mold from said nozzle is transmitted to the stationary platen and balanced with a force exerted thereon from the connection member, so that no bending moment is produced on the stationary platen.
The connection member may be supported on a base of the injection molding machine linearly movably only in the moving direction of the nozzle of the injection mechanism. The support member may be guided by a linear guide having a guide rail or a guide shaft, and the connection member may be supported linearly movably by the linear guide. Alternatively, the connection member may be supported by a leaf spring on the base of the injection molding machine.
The connection member may be formed into a U-shape having one end connected to the stationary platen and the other end connected the driving unit.
The driving unit may comprise a ball-screw mechanism having a ball-screw shaft and a ball-screw nut engaged with the ball-screw shaft, and a motor for driving the ball screw mechanism. In a preferable embodiment, the ball-screw shaft is supported by the connection member rotatably but unmovably relatively to the connection member and is driven by said motor, and the ball-screw nut is supported by the support member unrotatably. The motor may be mounted on the base of the injection molding machine or on the connection member.